1. Field of the Invention
The present invention relates to a controller for an automatic transmission which is mounted in a vehicle and controls gear shift by a motor.
2. Description of the Related Art
As this type of controller has been hitherto known a controller for a transmission shift operation device that is equipped with an electric motor for rotating the shift shaft of a transmission, performs F/B control on the basis of the difference between a target operation position calculated in a motor driving control circuit and an actual operation position to control the driving current of the electric motor, and drives the electric motor in a forward rotation or a reverse direction to enable a transmission shift operation (for example, see JP-A-2001-4023).
According to the related technique as described above, when the shift shaft of the transmission reaches the target operation position, the driving current to the electric motor is stopped, both the terminals of the armature of the electric motor are short-circuited to each other for a constant time to brake suddenly and stop the shift shaft at the target operation position, and then the short-circuiting concerned is released.
However, in the automatic transmission having the electric motor as described above, when the difference between the target operation position and the actual operation position is calculated and the F/B control (PID control) is performed on the basis of this difference, the driving current of the motor is controlled so that the shift shaft of the transmission is made to reach the target operation position as early as possible by increasing the F/B control gain. In this case, however, even when the actual operation position reaches the target operation position, both the terminals of the armature are short-circuited to each other to brake suddenly so that the shift shaft of the transmission can be stopped at the target operation position, the F/B gain is large and the driving force of the motor is increased. Consequently, the braking force for the sudden braking is insufficient, the shift shaft passes over the target operation position due to the inertia of the motor and thus gear shift time is lengthened.
Furthermore, when the shift shaft of the transmission reaches the target operation position, it is certainly necessary to short-circuit both the terminals of the armature for braking, and thus there is a problem that the short-circuit current occurs every gear shift and thus circuit elements and the electric motor are heated and deteriorated.